Howto:VOIP through NAT routers

Abstract

This page discusses NAT traversal of VOIP.

Introduction

VOIP signaling involves the exchange of IP addresses. Signaling addresses and media addresses RTP or T.38).

If the signaling crosses network borders you may get in trouble with private IP addresses. If a inside endpoint hands-out a private IP address (signaling or media) the external endpoint woun't be able to reach that IP address.

What WILL work

The only leliable way to get the hole thing working is to handle the problem on the private network. Make your private signaling endpoint never hand-out private IP addresses.

What you need

You need a Fullcone NAT router and a STUN server in the public network.

How to configure

Configure the public STUN server on your private signaling endpoint. It will use STUN to create a NAT mapping on the fullcone NAT router. It will then hand-out the mapped IP addresses (signaling and media) instead of the private ones.

What MAY work

What you need

You need a NAT router that at least do symmetric NAT.

How to configure

Nothing to do on the private equipment. The VIOP endpoints inside the private network will hand-out its private IP addresses.